Working of high tensile sheet metal



Feb. 1, 1949. L L. MARCHANT WORKING OF HIGH TENSILE SHEET METAL FiledMay 51, 1945 L155. L. MARCHANT Patented Feb. 1, 1949 UNITED STATESPATENT OFFICE WORKING OF HIGH TENSILE SHEET METAL Lee .L. Marchant,.Takoma Park, Md., assignor to Engineering and Research Corporation,Riverdale, Met, a corporation of Maryland Application May 31, 1945,Serial No. 596,887

v1 Claim. 1

'This 'invention relates to the dimpling, punching, shearing or otherworking of sheet metal and, more particularly, to the working of sheetmetal of-such high tensile strength that it tends to rupture or crackwhen worked col-d. While the invention is applicable to any such workingof high-tensile sheet metali't w'illbe described herein in connectionwith the dimpling of such sheet metal.

It has'zbeen found that if usual-and known dimplingrneans are utilizedto dimple high-tensile sheetm'etal', such as magnesium or high tensilevaluminum sheet, the metal surrounding the dimple will. crack andshatter when the pressure applied to the dimpling die is increasedsuiticiently to cause dimplingto take place. While it is known to reducetensile strength by heating in order to permit working, such methods andmeans for eiTecting-this as are presently available are not useful whereit is necessary to localize the heating or where rapid operation isnecessary or desirable.

The present invention provides a method of, and means for, dimplinghigh-tensile metal sheet without causing such cracking and rupturing. In

the method according to the invention the dimpling die is forced againstthe sheet with a known available pressure which is insufficient todimple the sheet while cold and is also insufficient to rupture or crackit. Simultaneously, the sheet is momentarily heated at and closelyadjacent the area of contact of the die until the tensile strength ofthe sheet at such area of contact is decreased to a value at which it isequal to or slightly less than, the pressure applied to the sheet by thedimpling means, at which time the die will dimple the sheet. The heatingis performed by the application of electric power to the sheet and inaccordance with the invention more than sufficient power to effect thenecessary heating is applied, whereby a very rapid increase intemperature at the area of contact is produced, thus localizing theheating and providing a very rapid operation.

In the drawings, in which similar reference numerals refer to likeparts,

Fig. 1 is a partly diagrammatic, partly sectional view showing parts ofa punching and riveting machine embodying the invention and showing theparts in their respective positions just prior to the dimpling andpunching operation, and

Fig. 2 is a view showing the parts illustrated in Fig. 1 aftercompletion of the dimpling and punching operation.

The high-tensile sheets with which the invention is particularly usefulare those which, when dimpled cold, will crack and shatter about thedimple because of the'high tensile strength of the material. Each suchmaterial has a so-called critical range which is defined, for the purposes of this application, as the temperature, or range temperature, ator below which the tensile strength of the material is such thatcracking or shattering will occur when the sheet is dinipled and abovewhich the tensile strength of the material is such that theseundesirable effects are not produced. For the purposes of thisapplication, the word cold will be understood to mean temperatures belowthis critical temperature or range.

In the drawings there are disclosed parts of a punching and rivetingmachine of known type and embodying means for carrying out my invention.The machine parts'comprise'a dimpling die 2 which is mounted on thelowerend of a vertical piston rod 4 which is movable vertically by apiston 6 mounted in a cylinder 3 to which fluid under pressure may beintroduced or exhausted through pipes IG, [2 in order to move the dimpling die. Below the dimpling die is mounted an anvil 20 having anopening therethrough in which a punch 22 is mounted for verticalmovement. These described parts are conventional and weilknown, beingdisclosed, for example, in my capending application Serial No. 535,134.In the operation of these known means, metal sheets 30 are placed on theanvil and the dimpling die is forced downwardly against them in order tosimultaneously dimple and punch the sheets.

Means are provided by the invention for momentarily heating the sheets30 during the application of the dimpling die thereto. Such meanscomprise an insulating member 49 which surrounds the anvil at the upperend thereof and supports a high-resistance contact member 62 whichextends above the upper end of the insulating member and the anvil andis adapted to support the sheets 30. Electric energy is adapted to besupplied to the contact member 42 through a connecting device 44 and tothe dimpling die 2 through connection 46.

In accordance with the invention cold sheets 30 of high-tensile sheetmetal are laid on the upper end of the contact member 42 and thedimpling die is forced downwardly against the sheets with a force whichis insufficient to dimple the sheets while cold and which is preferablyapproximately suilicient to dimple the sheet at the critical temperatureor critical range of tema peratures. As this pressure is insufficient tocause dimpling the parts will remain in the positions shown in Fig. 1.Contact between the dimpling die and the sheets will, however, com--plete the described electric circuit causing current to flow through thedimpling die, sheets and resistance member 42, and causing the sheets tobecome heated at and adjacent the area of contact of the dimpling die.In accordance with the invention the electric energy provided by thiscircuit closure is more than sufiicient to raise the temperature of thesaid localized area of the sheets to a value at which dimpling will takeplace without undesired rupture or shattering. The temperature of thesheets at this localized area will therefore be very rapidly increasedand the tensile strength very rapidly decreased.

When the tensile strength is decreased by in-- crease in temperature, toa value at which the pressure applied to the 'dimpling die is suflicientto dimple the sheet the dimpling will occur, after which the immediateremoval of the die 2 from the sheets will break the circuit and stop theheating. I have found that the surge of excess electric energy throughthe localized area of the sheets not only provides very rapid operationbut restricts the heating to the area at and closely adjacent the pointor area of contact between the dimpling die and the sheets. This permitsthe sheets to be held in the hand during the dimpling operation,although very high temperatures are produced at the dimpling area.

In the machine disclosed in the drawings, a punching operation isperformed simultaneously with the dimpling. This isusual in punching andriveting machines of known types and is well within the spirit and scopeof the invention.

While I have described and illustrated one method and means according tomy invention, modifications in such method and means may occur to thoseskilled in the art, all of which may be made without departing in anyway from the spirit and scope of the invention, for the limits of whichreference must be had to the appended claim.

What is claimed is:

The method of working metal, which metal has such a high tensilestrength that it tends to crack and shatter when worked cold, whichconsists in applying a working tool to the'metal with a pressureinsufficient to Work it in the desired manner while cold but which issuficient to work it in the desired manner at a temperature of the metaljust above the critical temperature thereof, and while maintaining suchpressure applying to the metal at the area of contact of the workingtool electric energy in amount more than sufflcient to cause the metalto be heated to a temperature at which the tensile strength is such thatthe pressure applied to the tool will cause the desired working.

LEE L. MARCHANT.

' of this patent:

UNITED STATES PATENTS Number Name Date 1,296,780 Dyer Mar. 11, 19191,333,036 Robertson et al. Mar. 9, 1920 1,658,056 Phelps et a1 Feb. 7,1928 1,670,699 Weed May 22, 1928 1,848,905 Rabezzand Mar. 8, 19321,870,987 Drake Aug. 9, 1932 2,066,791 McBain Jan. 5, 1937 FOREIGNPATENTS Number Country Date 245,232 Great Britain Jan. 7, 1926 375,882Italy Oct. 25, 1939

